<!DOCTYPE html>
<html lang="en">
<head>
	<meta charset="UTF-8">
	<meta name="viewport" content="width=device-width, initial-scale=1.0">
	<title>Document</title>
	<style>
		*{
			margin: 0;
			padding: 0;
			box-sizing: border-box;
		}
		@media screen and (min-width: 900px)  {
			ul{ 
				width: 25%;
				background: red;
				float: left;
			}
			.div1{
				width:50% ;
				background:blue;
				float: left;
			}
			.div2{
				width:25% ;
				float: left;
				background:yellow;
			}
			
		}
		
	</style>
</head>
<body>
	<ul>
		<li >11111111</li>
		<li></li>
		<li></li>
		<br>
	</ul>
	<h1></h1>
	<span><a且b>111</span>
	<div class="div1">11</div>
	<div class="div2">222</div>
	<br>1111</br>
	2222

<table border="1">
 <tr>
  <td>a</td>
 </tr>
 <tr>
  <td rowspan="2">b</td>
  <td>c</td>
 </tr>
</table>
</body>
</html>